[arkh]

https://www.ncbi.nlm.nih.gov/books/NBK222804/

> Research findings suggest that changes occur in the “biological clock” during adolescence. As a result, teenagers have a natural tendency to fall asleep later and to wake up later. This is referred to as sleep phase delay.

> A correlation was found between subjects' melatonin secretion and their stage of development. The results indicated that melatonin onset occurs later in adolescents, making it difficult for them to go to sleep earlier at night. At the same time, the hormone “turns off” later in the morning, making it harder for them to wake up early (Carskadon et al., 1998, 1999).

It's like things are happening to the body during puberty.